Lubricating oils used in passenger cars and heavy duty diesel engines have changed over the years. Today's engines are designed to run hotter and harder than in the past. Various additives have been added to lubricant formulations in order to reduce wear between moving parts. One particularly common antiwear additive is a zinc dialkyl dithiophosphate (“ZnDDP”). While such zinc compounds are particularly useful as antiwear agents, such zinc compounds may have one or more of the following disadvantages: increased levels of sulfur and/or phosphorus in the finished lubricant.
Future generations of passenger car motor oils and heavy duty diesel engine oils require lower levels of phosphorus and sulfur in the finished oil in order to protect pollution control devices as it is well known that sulfur and phosphorus containing additives may poison or otherwise reduce the effectiveness of pollution control devices. For example, current GF-4 motor oil specifications require a finished oil to contain less than 0.08 wt % and 0.7 wt % phosphorus and sulfur, respectively, and PC-10 motor oil specifications, the next generation heavy duty diesel engine oil, requires oils to contain less than 0.12 wt % and 0.4 wt % phosphorus and sulfur, respectively, and 1.0 wt % sulfated ash. Certain antiwear additives known in the industry contain phosphorus and sulfur at levels which reduce the effectiveness of pollution control devices.
Therefore, a need exists for lubricant additives and compositions that provide enhanced antiwear properties and which are more compatible with pollution control devices used for automotive and diesel engines. A need also exists for such lubricant additives and compositions which are more compatible with such pollution control devices without adversely affecting oil solubility, corrosion, and/or darkening the color of the finished lubricant. Such additives may contain phosphorus and/or sulfur and may be substantially devoid of molybdenum compounds.
In one embodiment herein is presented a lubricated surface including a base oil of lubricating viscosity, at least one metal salt of phosphorothioic acid, and an ashless, sulfur-free organophosphorus compound providing a metal to phosphorus weight ratio ranging from about 0.25:1 to about 1.0:1 by weight. The lubricant composition is substantially devoid of molybdenum.
In another embodiment, there is provided a vehicle having moving parts and containing a lubricant for lubricating the moving parts. The lubricant includes a base oil of lubricating viscosity, at least one metal salt of phosphorothioic acid, and an ashless, sulfur-free organophosphorus compound providing a metal to phosphorus weight ratio ranging from about 0.25:1 to about 1.0:1 by weight. The lubricant is substantially devoid of molybdenum.
In yet another embodiment there is provided a fully formulated lubricant composition including a base oil component of lubricating viscosity and an antiwear agent having at least one metal salt of phosphorothioic acid and an ashless, sulfur-free organophosphorus compound. The antiwear agent provides the lubricant composition with a metal to phosphorus weight ratio ranging from about 0.25:1 to about 1.0:1 by weight and a sulfur to phosphorus ratio ranging from about 0.5:1 to less than about 2.0:1 by weight. The lubricant composition is substantially devoid of molybdenum.
As set forth briefly above, embodiments of the disclosure provide a combination of an antiwear composition that includes a hydrocarbon soluble phosphoric acid metal salt and an ashless, sulfur-free organophosphorus compound that may significantly improve the antiwear properties of a lubricant composition and may enable a decrease in the amount of phosphorus and sulfur additives required for equivalent antiwear improving characteristics. The additive may be mixed with an oleaginous fluid that is applied to a surface between moving parts. The moving parts may be moving parts of an engine or transmission. Engine parts include parts of passenger car engines and heavy duty diesel engines. In other applications, the additive may be provided in a fully formulated lubricant composition. The additive is particularly directed to meeting the currently proposed GF-4 standards for passenger car motor oils and PC-10 standards for heavy duty diesel engine oils, as well as future passenger car and diesel engine oil specifications and standards.
An advantage of the embodiments described herein is that combinations of metal containing and ashless, sulfur-free phosphorus compounds surprisingly exhibit better wear performance than either component while also providing lower coefficients of friction. Other features and advantages of the compositions and methods described herein may be evident by reference to the following detailed description which is intended to exemplify aspects of the embodiments without intending to limit the embodiments described herein.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the embodiments disclosed and claimed.